angular - Get validators present in FormGroup/FormControl

Question

I'm using Material 2 in my app, but in this question I want to solve a problem specifically with Input.

As you can see in API Reference there's a property bind called required, which shows as asterisk in the placeholder.

So, I'm wondering if there's a way to check if the form control has an specific validator in Angular, because I really don't want to set manually for each input [required]="true/false"

I read the AbstractControl docs and I didn't find anything about it. I've encountered the hasError method (which ironically isn't documented in nowhere ... neither in FormGroup nor in FormControl nor in AbstractControl), however this is not what I'm looking for. It just checks if the form control has the error, but as you may have read, I want to check if the control has some specific validators...

Some code:

<md-input-container>
  <input placeholder="Placeholder" 
         mdInput [formControl]="anyCtrl" 
         [required]="anyCtrl.hasValidator('required')"> <!-- something like this -->
</md-input-container>

I hope the question is clear enough. Thanks in advance.

Answer 1

Angular doesn't really provide a great, clean way to do this, but it is possible. I think the validators are stored in a service that is injected into the FormBuilder(NG_VALIDATORS), and I'm going to look into hijacking that service or injecting it into a component, but for now this will work:

The docs and the source show a validator member on AbstractControl typed to ValidatorFn. ValidatorFn unfortunately simply has a null typing, so we can't see what's going on. However, after poking through the generated source and probing an app, it seems we can pass this validators method a control parameter, which will return an object of all validators present on that control, regardless of whether or not it's passing.

Strangely, this only works on the FormControl itself and not the FormGroup (on the FormGroup, the validators member is not a function and was always null in my testing). The compiled JS says this function takes a control parameter; I've tried passing in FormControl references but as far as I can tell it will just return the validators on the control as long as this parameter is not null.

Getting validators on a FormControl

// in the constructor
this.myForm = this.formBuilder.group({
  'anyCtrl': ['', Validators.required],
  'anotherCtrl': ['', Validators.compose([Validators.required, Validators.email])]
});

// later on 
let theValidators = this.myForm.controls['anyCtrl'].validator('');
console.log(theValidators) // -> {required: true};

let otherValidators = this.myForm.controls['anotherCtrl'].validator('');
console.log(otherValidators); // -> {required: true, email: true}

Making it easier to grab:

public hasValidator(control: string, validator: string): boolean {
  return !!this.myForm.controls[control].validator(control).hasOwnProperty(validator);
 // returns true if control has the validator
}

and in your markup:

<md-input-container>
  <input placeholder="Placeholder" 
         mdInput [formControl]="anyCtrl" 
         [required]="hasValidator('anyCtrl', 'email')">
</md-input-container>

Special case for Validators.required

The required validator has a shortcut. The [required] binding is actually an instance of the RequiredValidator directive (line 5022 of source/forms.js). This directive actually will add the required Validator to the FormControl it's on. It's equivalent to adding Validators.required to the FormGroup upon initialization. So, setting the bound property to false will remove the required Validator from that control and vice versa...either way, the directive affects the FormControl.required value, so binding it to a property that it changes won't really do much.

The only difference is that the [required] directive adds the asterisk to the placeholder while Validators.required does not.

I'm going to keep looking into NG_VALIDATORS, but I hope this helps for now!